Images are formed in silver halide color photographic materials by reaction between oxidized silver halide developing agent and a dye forming compound known as a coupler. It has become common practice to modify the photographic properties of the image, such as sharpness, granularity, contrast and color reproduction, by the use of an image modifying compound commonly referred to as a development inhibitor releasing (DIR) compound. Such materials were first described in U.S. Pat. Nos. 3,148,062 and 3,227,554.
More recently, U.S. Pat. Nos. 4,248,962; 4,409,323; 4,684,604; 5,034,311; and 5,055,385; and European Patent Application 0 167 168 have described release compounds from which a development inhibitor, or another photographically useful group, is released from an intervening group, called a timing group, after that group is released from the carrier portion of the compound. The use of a timing group provides a way to separate the release function from the carrier function and permits these separate functions to be separately designed into the compound.
In addition to development inhibitors, other photographically useful groups may desirably be released during photographic processing. Such groups include development accelerators, bleach accelerators, bleach inhibitors, complexing agents, toners, stabilizers, etc. Photographically useful groups typically are released during the development step in an imagewise manner. On occasion, depending upon the particular photographically useful group and the purpose it is to serve, it may be desired to release the group, in its active form, at a stage in the processing of the photographic element other than the development step, or in a uniform manner, or both.
A problem with the known release compounds is that the known timing groups are required to have high enough electron density to release the photographically useful group through either an intramolecular nucleophilic reaction or via an intramolecular electron migration. This requirement limits the choice of carrier groups to those whose pKa's are low enough to compensate for the high electron density of the timing group.
It would be desirable to provide release compounds which allow independent choice both of the photographically useful group and of the carrier group from which it is released. In addition it is desirable to have the release of the photographically useful group occur only when the timing group has been released from the carrier. Likewise, it is desirable to have the release of the photographically useful group not require an additional oxidation step.